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MANET Working Group Sanghyun Ahn
Internet Draft University of Seoul
Expires: June 13, 2016 December 22, 2015


DSR Extensions for the Resolution of Cached Route Reply Implosion
draft-ahn-manet-dsr-crri-00.txt

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Abstract

In DSR, a node can generate a route reply in response to a received
route request if it has a fresh route to the destination in its
route cache. However, this can incur the cached route reply problem
and DSR just tries to mitigate this problem by reducing the
possibility of cached route reply collisions. This document
describes how DSR can be extended for the resolution of the cached
route reply problem.


Table of Contents

1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Extensions on DSR Options Header . . . . . . . . . . . . . . . 3
3.1 Extensions on DSR Route Request Option . . . . . . . . . . . . 3
3.2 Extensions on DSR Acknowledgement Request Option . . . . . . . 4
3.3 Extensions on DSR Acknowledgement Option . . . . . . . . . . . 5
4. Other Considerations . . . . . . . . . . . . . . . . . . . . . 5
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6





























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1. Requirements notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].


2. Introduction

The DSR protocol [1] works based on the source routing mechanism
and support multiple routes between a source and destination node
pair by maintaining several routes in the route cache at the source.
However, in DSR, the route reply storm problem can happen
because of route replies generated by intermediate nodes with fresh
routes to the destination in their own route caches (i.e., cached
route replies). DSR tries to solve this route reply storm problem
by reducing the possibility of route reply collisions with adding
a short jitter delay before the broadcast of a route reply.
However, DSR does not try to resolve the cause of the route reply
storm problem.

The main reason of the route reply storm is uncontrolled
generation of route replies at intermediate nodes, i.e., cached
route replies. Therefore, a mechanism to control the generation of
route replies at intermediate nodes is required for the effective
operation of DSR. However,for the support of multipath routing,
too tight restriction (control) on route reply generation may not be
desirable. Therefore, when controlling the generation of route
replies, both of these aspects need to be considered. In this draft,
we describe how DSR Options header has to be extended to support
the control of generation route replies.


3. Extensions on DSR Options Header

In DSR, there is no way to control the generation of cached route
replies, so a C (Cached route reply) big is inserted in the DSR
Route Request option, To do that, the size of the Identification
field is reduced to 14 bits from 16 bits. This makes the
Acknowledgement Request option and the Acknowledgement option
modified because those two options have the Identification field.


3.1 Extensions on DSR Route Request Option

The Route Request option in the DSR Options header is extended as
follows:




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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Option Type | Opt Data Len | Identification |C| Resv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address[n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


IP fields: the same as described in [2]

Route Request fields: the same as described in [2] except for the
Identification field, the C bit and the
Resv field

Identification
The definition of this field is the same as that in [2].
Only the size of thie field is reduced to 12 bits.

C
C bit is used to indicate whether cached route replies are
allowed or not. C bit is set to 1 if the cached route reply
is allowed. The intermediate nodes can generate cached route
replies only when the C bit of the received Route Request option
is 1. Otherwise, only the destination node can generate
route replies.

Resv
The reserved field for further extensions on DSR Route Request
option.


3.2 Extensions on DSR Acknowledgement Request Option

The Acknowledgement Request option in the DSR Options header is
extended as follows:






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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len | Identification | Resv |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Identification
The definition of this field is the same as that in [2].
Only the size of thie field is reduced to 12 bits.

Resv
The reserved field for further extensions on DSR Acknowledgement
Request option.


3.3 Extensions on DSR Acknowledgement Option

The Acknowledgement option in the DSR Options header is extended
as follows:


0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len | Identification | Resv |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Identification
The definition of this field is the same as that in [2].
Only the size of thie field is reduced to 12 bits.

Resv
The reserved field for further extensions on DSR Acknowledgement
option.



4. Other Considerations

TBD.






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References

[1] D. Johnson, Y. Hu and D. Maltz, "The Dynamic Source Routing
Protocol," RFC 4728, February 2007.


Author's Address

Sanghyun Ahn
University of Seoul
90, Cheonnong-dong, Tongdaemun-gu
Seoul 130-743
Korea
Email: ahn@uos.ac.kr





































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